Solid-state imaging device, method for manufacturing the same, and electronic apparatus

ABSTRACT

A method for manufacturing a solid-state imaging device includes: forming pixels that receive incident light in a pixel array area of a substrate; forming pad electrodes in a peripheral area located around the pixel array area of the substrate; forming a carbon-based inorganic film on an upper surface of each of the pad electrodes including a connection surface electrically connected to an external component; forming a coated film that covers upper surfaces of the carbon-based inorganic films; and forming an opening above the connection surface of each of the pad electrodes to expose the connection surface.

FIELD

The present disclosure relates to a solid-state imaging device, a methodfor manufacturing the same, and an electronic apparatus.

BACKGROUND

An electronic apparatus, such as a digital camera, includes asolid-state imaging device. Examples of the solid-state imaging deviceinclude a CMOS (complementary metal oxide semiconductor) image sensorand a CCD (charge coupled device) image sensor.

In a solid-state imaging device, a pixel array area having a pluralityof pixels arranged in a matrix is provided on a surface of asemiconductor substrate. Each of the plurality of pixels is providedwith a photoelectric converter. The photoelectric converter is, forexample, a photodiode. A light receiving surface of the photodiodereceives light incident thereon via an optical system providedseparately from the imaging device, and signal charge is produced in aphotoelectric conversion process.

Among a variety of solid-state imaging devices, a CMOS image sensor isso configured that each pixel includes a plurality of transistors aswell as the photoelectric converter. The plurality of transistors readthe signal charge produced by the photoelectric converter and output thesignal charge in the form of an electric signal to a signal line.

A semiconductor device, such as a solid-state imaging device, isprovided with a pad electrode, which is provided to electrically connectthe semiconductor device to an external component. For example, thesemiconductor device is electrically connected to a board substrate, asemiconductor package, a semiconductor chip, or any other externalcomponent via the pad electrode.

The pad electrode is made, for example, of aluminum (Al). The padelectrode is alternatively made of an aluminum alloy containing silicon(Si), copper (Cu), and other elements.

For example, the semiconductor device, such as a solid-state imagingdevice, is electrically connected to an external device via the padelectrode by using a connection means, such as gold (Au)-based wirebonding and tin (Sn)-based solder reflow (see Japanese Patent Nos.3,158,466 and 3,959,710, for example).

When a contaminant is present on the surface of the pad electrode,electrical connection failure between the semiconductor device and anexternal device may occur in some cases. The electrical connectionfailure may cause the solid-state imaging device not to operatenormally, for example, to malfunction and eventually stop operating. Toavoid such a situation, the surface of the pad electrode is so cleanedthat any contaminant is removed.

For example, when layers provided on the pad electrode made of aluminumare dry etched by using a fluorine (F)-based etching gas, the fluorine(F) may become a contaminant on the pad electrode in some cases. Toremove the fluorine (F) left on the pad electrode, it has been proposedto clean the surface of the pad electrode with an organic amine-basedchemical solution (see “Investigation and Failure Analysis of“Flower-like” Defects on Microchip Aluminum Bondpads in WaferFabrication,” ICSE2006 Proc. 2006, pp. 626-629, for example).

Further, the pad metal of the pad electrode may melt and corrode,resulting in malfunction of the device in some cases. To avoid such asituation, it has been proposed to electrically connect thesemiconductor device to an external device via the pad electrode andthen form a carbon film that covers the semiconductor device, theexternal device, and a wiring line that connects them to each other (seeJP-A-3-83365 and JP-A-62-12163, for example).

SUMMARY

FIGS. 17A, 17B, 18C, and 18D show key steps of manufacturing asolid-state imaging device. FIGS. 17A, 17B, 18C, and 18D sequentiallyshow steps (a), (b), (c), and (d) of exposing the surface of a padelectrode 111P in the solid-state imaging device. FIGS. 17A, 17B, 18C,and 18D are cross-sectional views showing a portion of the solid-stateimaging device where the pad electrode 111P is formed.

A resist pattern RP is first formed, as shown in FIG. 17A.

Before forming the resist pattern RP, the pad electrode 111P is formed,for example, with aluminum, as shown in FIG. 17A. Components are thenprovided to cover the pad electrode 111P. Specifically, a passivationfilm 120, a planarization film 130, a lens material film 140, and anantireflection film 150 are sequentially provided on the upper surfaceof the pad electrode 111P. Although not shown, an on-chip lens is formedby using the lens material film 140 for each effective pixel in thepixel array area, where effective pixels are arranged, in thesolid-state imaging device. The on-chip lenses (not shown) are formed byusing the lens material film 140 made, for example, of a resin or anyother suitable organic material. In addition to the on-chip lenses, acolor filter (not shown) is formed for each effective pixel in the pixelarray area (see FIG. 9, which will be described later).

After the components are formed to cover the pad electrode 111P asdescribed above, the resist pattern RP is formed on the upper surface ofthe antireflection film 150.

In this example, after a photoresist film (not shown) is formed to coverthe upper surface of the antireflection film 150, the photoresist film(not shown) is patterned to form the resist pattern RP. Specifically,the resist pattern RP is formed by providing an opening KK1 through thephotoresist film in such a way that the opening KK1 exposes a portion ofthe upper surface of the pad electrode 111P.

The components provided on the upper surface of the pad electrode 111Pare then removed until the portion of the surface of the pad electrode111P is exposed, as shown in FIG. 17B.

In this step, the resist pattern RP is used as a mask, and theantireflection film 150, the lens material film 140, the planarizationfilm 130, and the passivation film 120 are sequentially dry etched. Anopening KK2 is thus provided, and the portion of the surface of the padelectrode 111P is exposed.

The components are dry etched, for example, by using a fluorine(F)-based etching gas, such as CF₄, C₂F₆, C₃F₈, CHF₃, and SF₆.

At this point, the exposed surface of the pad electrode 111P is damagedby the dry etching, and an etching damage portion DM is formed.

The resist pattern RP is then removed, as shown in FIG. 18C.

In this example, the resist pattern RP is removed from the upper surfaceof the antireflection film 150 by performing ashing.

The etching damage portion DM is then removed, as shown in FIG. 18D.

In this example, the etching damage portion DM is removed by performinga post-treatment of cleaning the surface of the pad electrode 111P. Thesurface of the pad electrode 111P is cleaned, for example, by using anorganic amine-based chemical solution.

In the solid-state imaging device, however, the cleaning described aboveerodes the on-chip lens (not shown) made of a resin and degrades thelens performance in some cases. For example, the height of the lens maybe reduced and the focal point is therefore shifted, or the surface ofthe lens may be changed and the amount of incident light is thereforereduced.

As a result, in the solid-state imaging device, the quality of capturedimages may be degraded in some cases.

Further, a contaminant may be left on the etching damage portion DM whenthe cleaning described above is performed improperly.

FIGS. 19A to 19C show the surface of the pad electrode resulting fromimproper cleaning. FIG. 19A is a photograph obtained by capturing animage of the upper surface of the pad electrode 111P, and FIGS. 19B and19C are enlarged SEM microphotographs obtained by capturing images ofcontaminants formed on the pad electrode 111P.

Circular contaminants are observed on the upper surface of the padelectrode 111P when it is left in the atmosphere, as shown in FIGS. 19Ato 19C.

When dry etching is performed (see FIG. 17B), the fluorine (F)-basedetching gas is converted into plasma and forms ions or radicals. Theresultant active fluorine (F) reacts with the aluminum that forms thepad electrode 111P to produce a compound of aluminum and fluorine(AlF_(x)). It is believed that the dry etching thus leaves activefluorine (F) on the pad electrode 111P and AlF_(x) is produced as acontaminant.

In particular, when the layers on the pad electrode 111P made of pure Alor an AlCu alloy are dry etched by using SF₆ or CHF₃ as an etching gas,a large number of contaminants may be produced in some cases.

FIGS. 20A to 20C show temporal change in the surface of the padelectrode. FIGS. 20A to 20C are photographs obtained by capturing imagesof the upper surface of the pad electrode 111P under an opticalmicroscope. FIG. 20A shows the upper surface immediately after the padelectrode is formed. FIG. 20B shows the upper surface left in theatmosphere for three days. FIG. 20C shows the upper surface left in theatmosphere for six days.

The contaminants grow to larger sizes with time, as shown in FIGS. 20Ato 20C.

FIGS. 21A to 21C show results of component analysis made on acontaminant. FIG. 21A is a SEM microphotograph showing a cross sectionof a contaminant, and FIGS. 21B and 21C show results of componentanalysis made on the contaminant. FIG. 21B shows a result of thecomponent analysis made at a point A, which is the center of thecontaminant, as shown in FIG. 21A. FIG. 21C shows a result of thecomponent analysis made at a point B, which is located in a lowerportion of the contaminant, as shown in FIG. 21A.

The contaminant contains not only aluminum (Al) but also fluorine (F),oxygen (O), and carbon (C), as shown in FIGS. 21B and 21C. From theresults described above, the mechanism according to which thecontaminant grows is speculated as follows.

The AlF_(x) produced as a contaminant on the pad electrode 111P made ofaluminum (Al) reacts with moisture in the atmosphere, and hydrogenfluoride (HF) is produced. Melted aluminum then reacts with the hydrogenfluoride (HF), and AlF_(x) is newly produced. The cycle is repeated andthe contaminant grows to a larger size.

That is, it is speculated that the contaminant grows when the reactionsexpressed by the following chemical formulae (1) and (2) (when x=3) arerepeated.

AlF₃+3H₂O→Al(OH)₃+3HF   (1)

Al+3F^(−→AlF) ₃+3e⁻  (2)

When AlF_(x) is present as a contaminant on the upper surface of the padelectrode 111P, the bond between the pad electrode 111P and anelectricity supplying metal configured as a connection means, such aswire bonding, is significantly degraded, sometimes resulting innon-ohmic connection or open connection.

As a result, the contaminant present on the surface of the pad electrode111P may cause the solid-state imaging device not to operate normally insome cases unless the cleaning has been performed properly.

Since the cleaning is, however, necessary in the manufacturing process,it is sometimes difficult to manufacture the device efficiently.

In addition to the above problem, in the solid-state imaging device,incident light may be reflected off the pad electrode 111P, and what iscalled a ghost phenomenon may occur, sometimes resulting in degradationin quality of captured images. Further, electro-migration andstress-migration phenomena may occur at the pad electrode, sometimesresulting in decrease in wiring reliability. Moreover, heat generationmay degrade reliability of the device in some cases.

As described above, it is sometimes difficult to improve the reliabilityand manufacturing efficiency of the solid-state imaging device.

It is therefore desirable to provide a solid-state imaging device, amethod for manufacturing the same, and an electronic apparatus thatallow improvement in reliability and manufacturing efficiency of thedevice.

A method for manufacturing a solid-state imaging device according to anembodiment of the present disclosure includes: forming pixels thatreceive incident light in a pixel array area of a substrate, forming padelectrodes in a peripheral area located around the pixel array area ofthe substrate, forming a carbon-based inorganic film on an upper surfaceof each of the pad electrodes including a connection surfaceelectrically connected to an external component, forming a coated filmthat covers upper surfaces of the carbon-based inorganic films, andforming an opening above the connection surface of each of the padelectrodes to expose the connection surface. The opening formation stepincludes forming a resist pattern on an upper surface of the coatedfilm, the resist pattern having openings corresponding to the connectionsurfaces and covering portions other than the connection surfaces,etching the coated film by using the resist pattern as a mask and thecarbon-based inorganic films as etching stopper films to expose portionsof the upper surfaces of the carbon-based inorganic films thatcorrespond to the connection surfaces, and performing ashing on theresist pattern and portions of the carbon-based inorganic films thatcorrespond to the connection surfaces to simultaneously remove theresist pattern and the portions.

A solid-state imaging device according to another embodiment of thepresent disclosure includes: a substrate having pixels that receiveincident light provided in a pixel array area, pad electrodes formed ina peripheral area located around the pixel array area of the substrate,a carbon-based inorganic film formed on an upper surface of each of thepad electrodes but other than a connection surface electricallyconnected to an external component, and a coated film that covers uppersurfaces of the carbon-based inorganic films and has openings formedabove the connection surfaces of the pad electrodes.

An electronic apparatus according to still another embodiment of thepresent disclosure includes: a substrate having pixels that receiveincident light provided in a pixel array area, pad electrodes formed ina peripheral area located around the pixel array area of the substrate,a carbon-based inorganic film formed on an upper surface of each of thepad electrodes but other than a connection surface electricallyconnected to an external component, and a coated film that covers uppersurfaces of the carbon-based inorganic films and has openings formedabove the connection surfaces of the pad electrodes.

In the embodiments of the present disclosure, a resist pattern is soformed on the upper surface of a coated film that the resist pattern hasopenings corresponding to the connection surfaces of the pad electrodesand covers portions other than the connection surfaces. The resistpattern is used as a mask and the carbon-based inorganic films are usedas etching stopper films to etch the coated film so that the portions ofthe upper surfaces of the carbon-based inorganic films that correspondto the connection surfaces are exposed. Ashing is then performed on theresist pattern and the portions of the carbon-based inorganic films thatcorrespond to the connection surfaces to remove the resist pattern andthe portions. As described above, the connection surfaces, which will beexposed, of the pad electrodes are covered with the carbon-basedinorganic films in the etching process. The connection surfaces of thepad electrodes are therefore not damaged in the etching process.

The embodiments of the present disclosure can provide a solid-stateimaging device, a method for manufacturing the same, and an electronicapparatus that allow improvement in reliability and manufacturingefficiency of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the configuration of a camera according toan embodiment of the present disclosure;

FIG. 2 shows an overall configuration of a solid-state imaging deviceaccording to the embodiment of the present disclosure;

FIG. 3 shows a key portion of the solid-state imaging device accordingto the embodiment of the present disclosure;

FIG. 4 shows a key portion of the solid-state imaging device accordingto the embodiment of the present disclosure;

FIG. 5 shows a key portion of the solid-state imaging device accordingto the embodiment of the present disclosure;

FIG. 6 shows a key portion of the solid-state imaging device accordingto the embodiment of the present disclosure;

FIG. 7 shows classification of amorphous carbon films;

FIGS. 8A and 8B diagrammatically show the structures of carbon-basedinorganic materials of which a carbon-based inorganic film is made inthe embodiment according to the present disclosure;

FIG. 9 shows a color filter CF according to the embodiment of thepresent disclosure;

FIGS. 10A to 10C are timing charts illustrating pulse signals suppliedto relevant components when a signal is read from a pixel P in theembodiment according to the present disclosure;

FIGS. 11A and 11B show a key portion formed in steps in a method formanufacturing the solid-state imaging device in the embodiment of thepresent disclosure;

FIGS. 12C and 12D show the key portion formed in steps in the method formanufacturing the solid-state imaging device in the embodiment of thepresent disclosure;

FIG. 13E shows the key portion formed in a step in the method formanufacturing the solid-state imaging device in the embodiment of thepresent disclosure;

FIG. 14 shows an overall configuration of a solid-state imaging devicewith no carbon-based inorganic film provided on the surface of each padelectrode;

FIGS. 15A and 15B diagrammatically show states in which incident light His incident on the two types of solid-state imaging device;

FIG. 16 diagrammatically shows a state in which current flows through apad electrode in the embodiment according to the present disclosure;

FIGS. 17A and 17B show key steps of manufacturing a solid-state imagingdevice;

FIGS. 18C and 18D show other key steps of manufacturing the solid-stateimaging device;

FIGS. 19A to 19C show the surface of a pad electrode resulting fromimproper cleaning;

FIGS. 20A to 20C show temporal change in the surface of the padelectrode; and

FIGS. 21A to 21C show results of component analysis made on acontaminant.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below withreference to the drawings.

(A) Configuration of Apparatus (A-1) Configuration of Key Portion ofCamera

FIG. 1 is a diagram showing the configuration of a camera 40 accordingto an embodiment of the present disclosure. FIG. 1 diagrammaticallyshows the overall configuration of the camera 40.

The camera 40 is an electronic apparatus and includes a solid-stateimaging device 1, an optical system 42, a control circuit unit 43, and asignal processing circuit unit 44, as shown in FIG. 1.

The solid-state imaging device 1 is disposed on the upper surface of asubstrate 501, as shown in FIG. 1. The solid-state imaging device 1 iselectrically connected to the substrate 501 with wires 502. Thesolid-state imaging device 1, which will be described later in detail,is provided with pad electrodes (not shown), which are electricallyconnected via the wires 502 to wiring lines (not shown) provided in thesubstrate 501.

A lid 503 is disposed above the solid-state imaging device 1. The uppersurface of the lid 503 has an opening, and the solid-state imagingdevice 1 receives incident light H incident as a subject image throughthe opening. The optical system 42 is disposed above the solid-stateimaging device 1. The incident light H incident through the opticalsystem 42 is received by an imaging surface PS and undergoesphotoelectric conversion. Signal charge is thus produced in thephotoelectric conversion. The solid-state imaging device 1, which isdriven based on a control signal outputted from the control circuit unit43, reads the signal charge and outputs it as raw data.

The optical system 42 includes lenses 421 a and 421 b and an IR cutofffilter 423, as shown in FIG. 1. In the optical system 42, the lenses 421a and 421 b are disposed in a lens holder 422. The IR cutoff filter 423is disposed on a lower surface of the lens holder 422. In the opticalsystem 42, the incident light H sequentially passes through the lenses421 a and 421 b and the IR cutoff filter 423 and reaches the imagingsurface PS of the solid-state imaging device 1.

The control circuit unit 43 outputs a variety of control signals to thesolid-state imaging device 1 and the signal processing circuit unit 44to control the operation thereof.

The signal processing circuit unit 44 performs signal processing on theraw data outputted from the solid-state imaging device 1 to produce adigital image of the subject image.

(A-2) Configuration of Key Portion of Solid-State Imaging Device

An overall configuration of the solid-state imaging device 1 will bedescribed.

FIG. 2 shows an overall configuration of the solid-state imaging device1 according to the embodiment of the present disclosure. FIG. 2 is a topview of the solid-state imaging device 1.

The solid-state imaging device 1 includes a substrate 101, as shown inFIG. 2. The substrate 101 is, for example, a semiconductor substratemade of silicon, and a pixel array area PA and a peripheral area SA areprovided on a surface of the substrate 101, as shown in FIG. 2.

The pixel array area PA has a rectangular shape and has a plurality ofpixels P arranged in the horizontal direction x and the verticaldirection y, as shown in FIG. 2. That is, the pixels P are arranged in amatrix. The pixels P will be described later in detail. The pixel arrayarea PA corresponds to the imaging surface PS shown in FIG. 1.

The peripheral area SA is located around the pixel array area PA, asshown in FIG. 2. In the peripheral area SA, a plurality of padelectrodes 111P are so provided that they surround the pixel array areaPA. Each of the pad electrodes 111P is provided with a carbon-basedinorganic film 300 in a portion other than a surface (square portion inFIG. 2) electrically connected to an external component.

Although not shown, the peripheral area SA is provided with peripheralcircuits.

For example, a vertical drive circuit, a column circuit, a horizontaldrive circuit, an external output circuit, and a timing generator areprovided as the peripheral circuits.

Specifically, the vertical drive circuit selects pixels P in the pixelarray area PA on a row basis and drives the selected pixels P. Thecolumn circuit performs signal processing on signals outputted frompixels P on a column basis. The column circuit includes a CDS(correlated double sampling) circuit (not shown) and performs signalprocessing for removing fixed pattern noise. The horizontal drivecircuit includes, for example, a shift register and sequentially outputssignals held in the column circuit for each column of pixels P to theexternal output circuit. The external output circuit performs signalprocessing on the signals outputted from the column circuit and outputsthe processed signals to an external component. The external outputcircuit includes, for example, an AGC (automatic gain control) circuitand an ADC circuit. The AGC circuit amplifies each of the signals, andthen the ADC circuit converts the analog signal into a digital signaland outputs the digital signal to an external component. The timinggenerator outputs a variety of timing signals to the componentsdescribed above, which are driven and controlled according to thecontrol signals.

In the present embodiment, the peripheral circuits are integrated withthe solid-state imaging device 1 but may alternatively be formed inother external devices.

(A-3) Detailed Configuration of Solid-State Imaging Device

The solid-state imaging device 1 according to the present embodimentwill be described in detail.

FIGS. 3 to 6 show key portions of the solid-state imaging device 1according to the embodiment of the present disclosure.

FIG. 3 diagrammatically shows the upper surface of the portion of thepixel array area PA where a pixel P is provided. FIG. 4 shows a circuitconfiguration of the pixel P. FIG. 5 is a cross-sectional viewdiagrammatically showing the portion described above. Specifically, FIG.5 is a cross-sectional view taken along the line X1-X2 shown in FIGS. 2and 3. FIG. 6 is a cross-sectional view of the portion of the peripheralarea SA where a pad electrode 111P is provided. Specifically, FIG. 6 isa cross-sectional view taken along the line X1 b-X2 b shown in FIG. 2.

In the pixel array area PA, each of the pixels P includes a photodiode21 and a pixel transistor Tr, as shown in FIGS. 3 and 4. The pixeltransistor Tr includes a transfer transistor 22, an amplifier transistor23, a selector transistor 24, and a reset transistor 25, reads signalcharge from the photodiode 21, and outputs the signal charge in the formof an electric signal.

In each of the pixels P, the photodiode 21 is provided in the substrate101, as shown in FIG. 5. Although not shown in FIG. 5, the pixeltransistor Tr shown in FIGS. 3 and 4 is provided in the front surface(upper surface in FIG. 5) of the substrate 101. A multilayer wiringlayer 111 is provided to cover the pixel transistor Tr, as shown in FIG.5. Further, above the multilayer wiring layer 111 are provided apassivation film 120, a planarization film 130, a color filter CF, anon-chip lens ML, and an antireflection film 150.

In each of the pixels P, the incident light H is incident downward,passes through the components described above, and received by a lightreceiving surface JS of the photodiode 21.

That is, the solid-state imaging device 1 of the present embodiment is a“front surface illumination” CMOS image sensor and receives the incidentlight H incident as a subject image through the front surface of thesubstrate 101 to capture a color image.

In the peripheral area SA, a wiring line in the uppermost layer thatforms part of the multilayer wiring layer 111 is provided as the padelectrode 111P, as shown in FIG. 6. Carbon-based inorganic films 300 arefurther provided in the peripheral area SA. The passivation film 120 andthe planarization film 130 are so provided that they cover themultilayer wiring layer 111 via the carbon-based inorganic films 300, asin the case of the pixel array area PA. No color filter CF or on-chiplens ML (see FIG. 5) is provided in the peripheral area SA. The lensmaterial film 140, which forms the on-chip lenses ML (see FIG. 5) in thepixel array area, is provided on the upper surface of the planarizationfilm 130 in the peripheral area SA. The antireflection film 150 is thenso provided that it covers the upper surface of the lens material film140.

The components that form the solid-state imaging device 1 will now bedescribed in detail.

(a) Photodiode 21

The photodiode 21 is disposed at a plurality of locations correspondingto the plurality of pixels P shown in FIG. 2. That is, the photodiodes21 are arranged across the imaging surface (xy plane) in the horizontaldirection x and the vertical direction y perpendicular to the horizontaldirection x.

Each of the photodiodes 21 is provided with the corresponding pixeltransistor Tr in a portion adjacent to the photodiode 21, as shown inFIG. 3.

Each of the photodiodes 21 has a grounded anode and is so configuredthat accumulated signal charge (electrons in this description) is readand outputted in the form of an electric signal by the pixel transistorTr to a vertical signal line 27, as shown in FIG. 4.

Each of the photodiodes 21 receives incident light H incident as asubject image, performs photoelectric conversion to produce signalcharge, and accumulates the signal charge, as shown in FIG. 5.

In this description, the incident light H incident through the frontsurface of the substrate 101 is received by the light receiving surfaceJS of the photodiode 21, as shown in FIG. 5. Above the light receivingsurface JS of the photodiode 21 are provided the multilayer wiring layer111, the passivation film 120, the planarization film 130, the colorfilter CF, the on-chip lens ML, and the antireflection film 150, asshown in FIG. 5. The photodiode 21 therefore receives the incident lightH incident sequentially through the components described above andperforms photoelectric conversion.

Each of the photodiodes 21 is provided in the substrate 101 made, forexample, of a single-crystal silicon semiconductor material, as shown inFIG. 5. Specifically, the photodiode 21 includes an n-type chargeaccumulation area. A hole accumulation area (not shown) is so formedthat dark current will not be produced at upper and lower interfaces ofthe n-type charge accumulation area. That is, the photodiode 21 has whatis called an HAD (hole accumulated diode) structure.

Although not shown, the substrate 101 is provided with a pixel separator(not shown) that separates the plurality of pixels P from each other,and the photodiodes 21 are disposed in the areas separated by the pixelseparator.

(b) Pixel Transistor Tr

The pixel transistor Tr is disposed at a plurality of locationscorresponding to the plurality of pixels P shown in FIG. 2.

Each of the pixel transistors Tr includes the transfer transistor 22,the amplifier transistor 23, the selector transistor 24, and the resettransistor 25, reads signal charge from the photodiode 21, and outputsthe signal charge in the form of an electric signal, as shown in FIGS. 3and 4. For example, the pixel transistor Tr is positioned below thephotodiode 21 in the imaging surface (xy plane), as shown in FIG. 3.

The transistors 22 to 25 that form the pixel transistor Tr are disposedin the front surface of the substrate 101, although not shown in FIG. 5.Each of the transistors 22 to 25 is, for example, an N-channel MOStransistor having a gate made, for example, of polysilicon. Thetransistors 22 to 25 are covered with the multilayer wiring layer 111.

(b-1) Transfer Transistor 22

In each of the pixel transistors Tr, the transfer transistor 22transfers signal charge produced by the photodiode 21 to a floatingdiffusion node FD, as shown in FIGS. 3 and 4.

Specifically, the transfer transistor 22 is disposed between the cathodeof the photodiode 21 and the floating diffusion node FD, as shown inFIGS. 3 and 4. A transfer line 26 is electrically connected to the gateof the transfer transistor 22. When a transfer signal TG is sent throughthe transfer line 26 to the gate of the transfer transistor 22, signalcharge accumulated in the photodiode 21 is transferred to the floatingdiffusion node FD.

(b-2) Amplifier Transistor 23

In each of the pixel transistors Tr, the floating diffusion node FDconverts the charge into voltage, and the amplifier transistor 23amplifies the resultant electric signal and outputs the amplifiedsignal, as shown in FIGS. 3 and 4.

Specifically, the amplifier transistor 23 is disposed between theselector transistor 24 and the reset transistor 25, as shown in FIG. 3.In this description, the gate of the amplifier transistor 23 iselectrically connected to the floating diffusion node FD, as shown inFIG. 4. The drain of the amplifier transistor 23 is electricallyconnected to a power supply line Vdd, and the source of the amplifiertransistor 23 is electrically connected to the selector transistor 24.The amplifier transistor 23 is supplied with fixed current from a fixedcurrent source I and operates as a source follower when the selectortransistor 24 is selected to be turned on. The amplifier transistor 23therefore amplifies the electric signal from the floating diffusion nodeFD, which has converted the charge into voltage, when a selection signalis supplied to the selector transistor 24.

(b-3) Selector Transistor 24

In each of the pixel transistors Tr, the selector transistor 24, whenreceiving the selection signal, outputs the electric signal outputtedfrom the amplifier transistor 23 to the vertical signal line 27, asshown in FIGS. 3 and 4.

Specifically, the selector transistor 24 is disposed adjacent to theamplifier transistor 23, as shown in FIG. 3. An address line 28, throughwhich the selection signal is supplied, is connected to the gate of theselector transistor 24, as shown in FIG. 4. The selector transistor 24is turned on when the selection signal is supplied thereto and outputsthe output signal having been amplified by the amplifier transistor 23as described above to the vertical signal line 27.

(b-4) Reset Transistor 25

In each of the pixel transistors Tr, the reset transistor 25 resets thepotential of the gate of the amplifier transistor 23, as shown in FIGS.3 and 4.

Specifically, the reset transistor 25 is disposed adjacent to theamplifier transistor 23, as shown in FIG. 3. A reset line 29, throughwhich a reset signal is supplied, is electrically connected to the gateof the reset transistor 25, as shown in FIG. 4. The drain of the resettransistor 25 is electrically connected to the power supply line Vdd,and the source of the reset transistor 25 is electrically connected tothe floating diffusion node FD. The reset transistor 25, when the resetsignal is supplied to the gate thereof through the reset line 29, resetsthe potential of the gate of the amplifier transistor 23 to the powersupply voltage via the floating diffusion node FD.

In the above description, the transfer line 26, the address line 28, andthe reset line 29 are so wired that they are connected to the gates ofthe transistors 22, 24, and 25 associated with a plurality of pixels Parranged in the horizontal direction H (row direction). The transistors22, 23, 24, and 25 described above associated with the pixels Pcorresponding to a single row therefore simultaneously operate.

(c) Multilayer Wiring Layer 111 (Including Pad Electrode 111P)

The multilayer wiring layer 111 is disposed on the front surface of thesubstrate 101, as shown in FIGS. 5 and 6.

The multilayer wiring layer 111 includes wiring lines 111 h and aninsulating layer 111 z. In the insulating layer 111 z, the wiring lines111 h are so formed that they are electrically connected to a variety ofdevices.

In this description, the wiring lines 111 h are so formed and stacked inthe pixel array area PA that they function as the transfer line 26, theaddress line 28, the vertical signal line 27, the reset line 29, andother lines shown in FIG. 4. The wiring lines 111 h are disposed, forexample, along the boundary between the pixels P and electricallyconnected via holes (not shown) as appropriate.

On the other hand, in the peripheral area SA, the pad electrodes 111Pare provided on the multilayer wiring layer 111, as shown in FIG. 6. Thepad electrodes 111P are so formed that they are electrically connectedto wiring lines (not shown) in the uppermost layer of the multilayerwiring layer 111. The pad electrodes 111P are so provided in theperipheral area SA that they surround the pixel array area PA, as shownin FIG. 2.

Each of the pad electrodes 111P is made, for example, of aluminum (Al)as the wiring lines 111 h are. The pad electrode 111P is not necessarilymade of aluminum (Al) but may alternatively be made of an aluminum alloycontaining, for example, silicon (Si) and copper (Cu). Further, titanium(Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN),titanium tungsten (TiW), tungsten nitride (WN), or any other refractorymetal may be provided as a barrier metal portion above and below thealuminum or aluminum alloy portion.

An opening KK is provided above each of the pad electrodes 111P, asshown in FIG. 6. The opening KK is formed to expose the surface of thepad electrode 111P that is electrically connected to an externalcomponent. That is, a wire 502 is electrically connected to the exposedsurface of the pad electrode 111P, as shown in FIG. 1, whereby thesolid-state imaging device 1 is electrically connected to the substrate501.

The carbon-based inorganic film 300 is then so provided that it coverspart of the pad electrode 111P, as shown in FIG. 6.

(d) Carbon-based Inorganic Film 300

The carbon-based inorganic film 300 is provided on the surface of thepad electrode 111P but only on the portion where the opening KK is notprovided, as shown in FIG. 6. That is, the opening KK is formed throughthe carbon-based inorganic film 300 in the portion corresponding to thesurface of the pad electrode 111P that is electrically connected to anexternal component.

In the present embodiment, the carbon-based inorganic film 300 preventsthe incident light H from being reflected off the surface of the padelectrode 111P. That is, the material and thickness of the carbon-basedinorganic film 300 are so selected as appropriate that opticalinterference provides an antireflection function.

The carbon-based inorganic film 300, which will be described later indetail, is also used as an etching stopper film when the layers providedon the carbon-based inorganic film 300 are dry etched. In thisdescription, in a dry etching process using a fluorine (F)-based gas,the carbon-based inorganic film 300, which is made of a material thatunlikely reacts with activated fluorine (F) ions or radicals, functionsas an etching stopper film.

The carbon-based inorganic film 300 is a film made of an inorganicmaterial primarily containing carbon, specifically, at least one ofgraphite, graphene, carbon nanotubes, and diamond-like carbon (amorphouscarbon).

FIG. 7 shows classification of amorphous carbon films.

FIGS. 8A and 8B diagrammatically show the structures of carbon-basedinorganic materials of which the carbon-based inorganic film 300 is madein the embodiment according to the present disclosure. FIG. 8A shows thestructure of graphite, and FIG. 8B shows the structure of diamond-likecarbon. In FIGS. 8A and 8B, a white circle represents a carbon (C)element, and a thick line represents the bond between carbon elements.

Graphite includes a layer having a crystal structure based on sp²-bondedcarbon elements, as shown in FIGS. 7 and 8A. In graphite, the layer isstacked multiple times, and Van der Waals attraction bonds the multiplelayers to each other, whereby conductivity is achieved. Graphene doesnot include a plurality of layers formed of sp²-bonded carbon elementsbut includes a sp²-bonded monolayer having a thickness corresponding toonly a single carbon atom. Graphene is therefore a two-dimensionalmaterial having excellent conductivity. A carbon nanotube is obtained byrolling a graphene sheet or graphene sheets to form a coaxially tubularmaterial.

Diamond-like carbon (amorphous carbon) is non-crystalline carbon, whichis not crystallized, and a mixture of a portion containing sp³-bondedcarbon elements and a portion containing sp²-bonded carbon elements, asshown in FIGS. 7 and 8B.

When the carbon-based inorganic film 300 is made of diamond-like carbon,the proportion of sp³-bonded carbon-carbon structure may be at least 5%of all carbon-carbon bonded structures.

In this description, it is particularly optimum to form the carbon-basedinorganic film 300 with diamond-like carbon in which the proportion ofsp³-bonded carbon-carbon structures is at least 40% of all carbon-carbonbonded structures (sp³ bond>sp² bond).

The reason for this is that when the number of sp³ bonded structures isgreater than the number of sp² bonded structures, the resultant materialhas high hardness, high transparency, and low conductivity.

Further, the carbon-based inorganic film 300 may be made of a materialhaving a hydrogen (H) content of several percents (5%, for example) orlower.

The reason for this is that a material primarily containing carbon and afairly large amount of hydrogen (H) element is an organic material,which reacts in the dry etching process and degrades the durability ofthe material, and hence is not suitably used as an etching stopper film.

The carbon-based inorganic film 300 is therefore preferably made of a-Cor ta-C shown in FIG. 7. On the other hand, it is not preferable to formthe carbon-based inorganic film 300 with a-C:H or ta-C:H shown in FIG.7.

Further, among the materials primarily containing carbon shown in FIG.7, glassy carbon is a bulk material, and pylorite carbon is a carbonprecursor obtained by thermally decomposing an organic material and isnot a thin film forming material. Glassy carbon or pylorite carbon istherefore not used to form the carbon-based inorganic film 300.

(e) Passivation Film 120

The passivation film 120 is provided on the multilayer wiring layer 111in the pixel array area PA, as shown in FIG. 5.

In the peripheral area SA, the passivation film 120 is provided abovethe multilayer wiring layer 111 with the carbon-based inorganic film 300therebetween, as shown in FIG. 6. The opening KK is formed through thepassivation film 120 in the portion corresponding to the surface of thepad electrode 111P that is electrically connected to an externalcomponent.

The passivation film 120 is made, for example, of a silicon nitride(Si_(x)N_(y)). The passivation film 120 may be a monolayer made of asilicon nitride (Si_(x)N_(y)), or a silicon oxide (SiO₂) layer may bestacked thereon for stress relaxation.

(f) Planarization Film 130

The planarization film 130 is provided above the multilayer wiring layer111 with the passivation film 120 therebetween in the pixel array areaPA and the peripheral area SA, as shown in FIGS. 5 and 6. Theplanarization film 130 is made, for example, of a resin or any othersuitable organic material.

The planarization film 130 is provided to planarize an irregular surfaceof the passivation film 120.

In the peripheral area SA, the opening KK is formed through theplanarization film 130 in the portion corresponding to the surface ofthe pad electrode 111P that is electrically connected to an externalcomponent, as shown in FIG. 6, as in the case of the passivation film120.

(g) Color Filter CF

The color filter CF is provided above the multilayer wiring layer 111with the passivation film 120 and the planarization film 130therebetween in the pixel array area PA, as shown in FIG. 5. The colorfilter CF, when provided on the surface planarized by the planarizationfilm 130, is so formed that it precisely faces the light receivingsurface JS of the photodiode 21. Further, the planarization film 130ensures tight contact of the color filter CF.

No color filter CF is provided in the peripheral area SA, as shown inFIG. 6.

FIG. 9 shows the color filter CF in the embodiment according to thepresent disclosure. FIG. 9 is a top view of the color filter CF.

The color filter CF, which is provided to each of the plurality ofpixels P as shown in FIG. 9, colors the incident light H and transmitthe colored light toward the light receiving surface JS.

The color filter CF includes a red filter layer CFR, a green filterlayer CFG, and a blue filter layer CFB, as shown in FIG. 9.

In the color filter CF, the red filter layer CFR has high opticaltransmittance across a wavelength band corresponding to red (625 to 740nm, for example), colors the incident light H red, and transmits thecolored light toward the light receiving surface JS. The green filterlayer CFG has high optical transmittance across a wavelength bandcorresponding to green (500 to 565 nm, for example) , colors theincident light H green, and transmits the colored light toward the lightreceiving surface JS. The blue filter layer CFB has high opticaltransmittance across a wavelength band corresponding to blue (450 to 485nm, for example), colors the incident light H blue, and transmits thecolored light toward the light receiving surface JS.

The red filter layer CFR, the green filter layer CFG, and the bluefilter layer CFB are disposed adjacent to one another and correspond tothe plurality of respective pixels P.

In this description, the red filter layer CFR, the green filter layerCFG, and the blue filter layer CFB are arranged in a Bayer layout, asshown in FIG. 9. That is, the green filter layers CFG are diagonallyarranged in a checkered pattern. The red filter layers CFR and the bluefilter layers CFB are then diagonally arranged with respect to the greenfilter layers CFG.

For example, each of the filter layers CFR, CFG, and CFB is formed, forexample, by applying an application liquid containing a coloring pigmentand a photoresist resin by using spin coating or any other coatingmethod to form a coated film and patterning the coated film by usinglithography.

As described above, the color filter CF transmits light fluxes havingdifferent colors in such a way that adjacent pixels P arranged in thehorizontal direction x and the vertical direction y receive thedifferent-color light fluxes.

The color filter CF is not necessarily an RGB primary color filter butmay alternatively be a complementary color filter formed of yellow,magenta, cyan filter layers.

(h) On-Chip Lens ML and Lens Material Layer 140

The on-chip lenses ML are provided above the multilayer wiring layer 111with the passivation film 120, the planarization film 130, and the colorfilter CF therebetween in the pixel array area PA, as shown in FIG. 5.The on-chip lenses ML are so provided that they correspond to the pixelsP in the pixel array area PA and are formed by processing the lensmaterial film 140.

Each of the on-chip lenses ML is a convex lens protruding convexlyupward and focuses the incident light H on the corresponding photodiode21. That is, each of the on-chip lenses ML is so formed that thethickness at the center is greater than the thickness at the edge in adirection z perpendicular to the light receiving surface JS.

No on-chip lens ML is provided in the peripheral area SA, and the lensmaterial film 140, which forms the on-chip lenses ML in the pixel arrayarea PA, is provided above the multilayer wiring layer 111 with thepassivation film 120 and the planarization film 130 therebetween, asshown in FIG. 6. The opening KK is formed through the lens material film140 in the portion corresponding to the surface of the pad electrode111P that is electrically connected to an external component.

For example, the on-chip lenses ML and the lens material film 140 aremade of a resin or any other suitable organic material.

In the above description, the on-chip lenses ML are directly formed onthe color filter CF but are not necessarily formed this way. When theformation of the color filter CF produces large steps, anotherplanarization film (not shown) may be provided to planarize the steps,and the on-chip lenses ML may be formed on the thus planarized surface.Further, in the above description, the on-chip lenses ML are so formedthat the center of each of the on-chip lenses ML coincides with thecenter of the corresponding light receiving surface JS but the on-chiplenses ML are not necessarily formed this way.

(i) Antireflection Film 150

The antireflection film 150 is so provided that it covers the uppersurfaces of the on-chip lenses ML and the lens material film 140 in thepixel array area PA, as shown in FIG. 5.

In the peripheral area SA, the antireflection film 150 is so providedthat it covers the upper surface of the lens material film. 140, asshown in FIG. 6. The opening KK is formed through the antireflectionfilm 150 in the portion corresponding to the surface of the padelectrode 111P that is electrically connected to an external component.

The antireflection film 150 prevents the incident light H from beingreflected off the surfaces of the on-chip lenses ML and the lensmaterial film 140, as shown in FIGS. 5 and 6. That is, the material andthickness of the antireflection film 150 is so selected as appropriatethat optical interference provides an antireflection function.

In general, the antireflection film 150 is made of a material having arefractive index lower than that of the on-chip lenses ML. For example,the antireflection film 150 is made of a silicon oxide (refractive indexn=1.4). The antireflection film 150 may alternatively be formed bystacking a plurality of layers having different refractive indices. Theantireflection film 150 can be formed as appropriate in consideration ofdesired performance, cost, and other factors.

(j) Others

FIGS. 10A to 10C are timing charts illustrating pulse signals suppliedto relevant components when a signal is read from a pixel P in theembodiment according to the present disclosure. FIG. 10A shows theselection signal (SEL) inputted to the gate of the selector transistor24. FIG. 10B shows the reset signal (RST) inputted to the gate of thereset transistor 25. FIG. 10C shows the transfer signal (TG) inputted tothe gate of the transfer transistor 22 (see FIG. 4).

As shown in FIGS. 10A to 10C, the selection signal (SEL) is firstchanged from a low level to a high level at a first point of time t1sothat the selector transistor 24 (see FIG. 4) is turned on. The resetsignal (RST) is then changed from a low level to a high level at asecond point of time t2 so that the reset transistor 25 (see FIG. 4) isturned on, which resets the potential of the gate of the amplifiertransistor 23 (see FIG. 4).

The reset signal (RST) is then changed from the high level to the lowlevel at a third point of time t3 so that the reset transistor 25 isturned off. A voltage corresponding to the reset level is then read asan output signal, which is sent to the column circuit (not shown).

The transfer signal (TG) is then changed from a low level to a highlevel at a fourth point of time t4 so that the transfer transistor 22 isturned on, which allows signal charge accumulated in the photodiode 21to be transferred to the gate of the amplifier transistor 23.

The transfer signal (TG) is then changed from the high level to the lowlevel at a fifth point of time t5 so that the transfer transistor 22 isturned off. A voltage corresponding to a signal level according to theamount of the accumulated signal charge is then read as an outputsignal, which is sent to the column circuit (not shown).

In the column circuit (not shown), the reset level having been readearlier and the signal level having been read later undergo asubtraction process, and the resultant signal is accumulated. In thisway, fixed pattern noise resulting, for example, from variation in Vthof each of the transistors associated with each of the pixels P iscanceled.

As described above, the pixels P arranged in each row in the horizontaldirection x are simultaneously driven because the gates of thetransistors 22, 24, and 25 associated with the pixels P are connected ona row basis. That is, the pixels P are sequentially selected in thevertical direction on a horizontal line (pixel row) basis.

The variety of timing signals then control the transistors associatedwith each of the pixels P, whereby an output signal from the pixel P isread to the column circuit (not shown) via the vertical signal line 27.This operation is performed on a column basis. The signals accumulatedin the column circuit (not shown) are then sequentially selected by thehorizontal drive circuit (not shown) and outputted to the externaloutput circuit (not shown).

(B) Manufacturing Method

Key steps of a method for manufacturing the solid-state imaging device 1described above will be described below.

FIGS. 11A, 11B, 12C, 12D, and 13E show a key portion formed in steps inthe method for manufacturing the solid-state imaging device 1 in theembodiment of the present disclosure.

FIGS. 11A, 11B, 12C, 12D, and 13E sequentially show steps (a), (b), (c),(d), and (e) of exposing part of the surface of a pad electrode 111P inthe solid-state imaging device 1. Each of the figures is across-sectional view showing the portion of the peripheral area SA ofthe solid-state imaging device 1 where the pad electrode 111P is formed.That is, each of the figures is a cross-sectional view taken along theline X1 b-X2 b shown in FIG. 2, as in FIG. 6. Further, each of thefigures selectively shows a portion above the portion where the padelectrode 111P is formed.

(a) Formation of Pad Electrode 111P and Other Components

The pad electrode 111P and other components are first formed, as shownin FIG. 11A.

In the following description, the pad electrodes 111P are provided inthe peripheral area SA, as shown in FIG. 11A. Specifically, after ametal film is formed, the metal film is patterned to form the padelectrodes 111P. The carbon-based inorganic film 300 is then so providedthat it covers the upper surface of each of the pad electrodes 111P. Thepassivation film 120, the planarization film 130, the lens material film140, and the antireflection film 150 are then sequentially so providedon the upper surfaces of the pad electrodes 111P that they cover the padelectrodes 111P.

The components described above are formed, for example, under thefollowing conditions.

[Pad Electrode 111P]

-   material: aluminum or aluminum alloy-   thickness: 300 to 1200 nm (depending on device performance)

[Carbon-Based Inorganic Film 300]

-   material: graphite, graphene, carbon nanotube, or diamond-like    carbon (amorphous carbon)-   thickness: 10 to 50 nm (or thickness corresponding to a single    carbon element when graphene is used)

[Passivation Film 120]

-   material: silicon nitride (Si_(x)N_(y)) or any other suitable    material-   thickness: 200 to 800 nm (depending on composition)

[Planarization Film 130]

-   material: acrylic resin or epoxy resin-   thickness: 50 to 800 nm (depending on composition, material, and    shape)

[Lens Material Film 140]

-   material: acrylic resin or epoxy resin-   thickness: 200 to 2000 nm (depending on composition and material)

[Antireflection Film 150]

-   material: silicon oxide (SiO₂) or any other suitable material-   thickness: 50 to 250 nm (depending on composition and material)

Although not shown in FIG. 11A, the wiring lines 111 h in the uppermostlayer are formed in the pixel array area PA as well as the pad electrode111P, as shown in FIG. 5. After the passivation film 120 and theplanarization film 130 are formed, the color filter CF is formed on theupper surface of the planarization film 130. After the lens materialfilm 140 is then so formed that it covers the color filter CF, part ofthe lens material film 140 is processed into the on-chip lenses ML. Theon-chip lenses ML are formed, for example, by using a reflow method, anetch-back method, an imprint method, or any other suitable formingmethod. Thereafter, the antireflection film 150 is so provided that itcovers the on-chip lenses ML and the lens material film 140.

(b) Formation of Photoresist Film PR

The photoresist film PR is then formed, as shown in FIG. 11B.

In this description, a photoresist film PR is formed by using spincoating to apply a photoresist material in such a way that it covers theupper surface of the antireflection film 150, as shown in FIG. 11B.

(c) Formation of Resist Pattern RP

A resist pattern RP is then formed, as shown in FIG. 12C.

In this description, the resist pattern RP is formed by patterning thephotoresist film PR (see FIG. 11B). Specifically, the resist pattern RPis formed by providing an opening KK1 above the portion of the uppersurface of each of the pad electrodes 111P that is exposed (see FIG. 6).

For example, the resist pattern RP is so formed that the side surface ofthe opening KK1 is perpendicular to the imaging surface (xy plane) asshown in FIG. 12C. The resist pattern RP may alternatively be so formedthat the side surface of the opening KK1 is inclined or tapered withrespect to the imaging surface (xy plane). When a plurality of films areetched, the resist pattern RP preferably has tapered openings becausethe resultant shape thereof has a relatively small amount of sideetching.

(d) Etching of Components Provided on Upper Surface of Carbon-BasedInorganic Film 300

The components provided on the upper surface of each of the carbon-basedinorganic films 300 are then etched until part of the surface of thecarbon-based inorganic film 300 is exposed, as shown in FIG. 12D.

In this description, the resist pattern RP is used as a mask to removethe antireflection film 150, the lens material film 140, theplanarization film 130, and the passivation film 120 in a dry etchingprocess so that part of the surface of the carbon-based inorganic film300 is exposed.

For example, the components described above are dry etched by using afluorine (F)-based etching gas containing at least one of CF₄, C₂F₆,C₃F₈, CHF₃, and SF₆. The dry etching may be performed with oxygen (O),argon (Ar), and any other suitable gas introduced as appropriate. Thegases described above are converted into plasma to form active ions orradicals, which chemically react with the antireflection film 150 andother films to be etched, whereby the film are etched.

In the thus performed dry etching process, the antireflection film 150,the lens material film 140, the planarization film 130, and thepassivation film 120 are etched. That is, portions of the antireflectionfilm 150, the lens material film 140, the planarization film 130, andthe passivation film 120 that correspond to the bottom of the openingKK1 (see FIG. 12C) formed through the resist pattern RP are removed,whereby an opening KK2 is formed through the components described above.

For example, the dry etching is performed by using an ICP etcher underthe following conditions.

-   gas pressure: 0.3 to 2.0 Pa-   gas flow rate:    -   O₂: 50 to 500 scc    -   CHF₃: 0 to 50 scc    -   CF₄: 30 to 400 scc    -   Ar: 0 to 30 scc-   discharge (plasma) power: 500 to 2000 W-   bias power: 20 to 500 W

The carbon-based inorganic film 300 under the passivation film 120 isetched at an extremely slow rate in the dry etching process. Thecarbon-based inorganic film 300 therefore functions as an etchingstopper, whereby the dry etching will not proceed farther.

In the dry etching process described above, the plurality of films to beetched may be removed all together or separately.

To further increase etching precision in the dry etching processdescribed above, it is preferable to detect an endpoint by using an endpoint detector (EPD). The films located above the carbon-based inorganicfilm 300 so that they are etched are made, for example, of inorganicsilicon nitrides. It is therefore possible to detect an end pointaccurately and terminate the dry etching process by monitoring lightemitted from a silicon-based gas resulting from the films to be etched.

(e) Removal of Resist Pattern RP and Part of Carbon-Based Inorganic Film300

The resist pattern RP and part of the carbon-based inorganic film 300are then removed, as shown in FIG. 13E.

In this description, the resist pattern RP is removed from the uppersurface of the antireflection film 150 by performing O₂ plasma-basedashing. Part of the carbon-based inorganic film 300 is removedsimultaneously with the resist pattern RP.

Specifically, the carbon-based inorganic film 300 is removed from partof the surface of the pad electrode 111P in accordance with thefollowing reactions, whereby the opening KK is formed through thecarbon-based inorganic film 300.

C+O*→CO   (3)

C+20*→CO₂   (4)

As a result, the pad electrode 111P is exposed in the portion where theopening KK has been formed.

Thereafter, the wires 502 are electrically connected to the exposedsurfaces of the pad electrodes 111P, as shown in FIG. 1, whereby thesolid-state imaging device 1 is electrically connected to the substrate501.

(C) Overview

As described above, in the present embodiment, the pixels P, whichreceive the incident light H, are formed in the pixel array area PA ofthe substrate 101 (pixel formation step). Further, the pad electrodes111P are formed in the peripheral area SA located around the pixel arrayarea PA of the substrate 101 (pad electrode formation step) . In thepresent embodiment, the pad electrodes 111P are made of aluminum or analuminum alloy. The carbon-based inorganic film 300 is then formed onthe upper surface of each of the pad electrodes 111P including theconnection surface electrically connected to an external component(carbon-based inorganic film formation step). In the present embodiment,the carbon-based inorganic film 300 is made of at least one of graphite,graphene, carbon nanotube, and diamond-like carbon (amorphous carbon).The passivation film 120, the planarization film 130, the lens materialfilm 140, the antireflection film 150, and other coated films are thenso formed that they cover the upper surfaces of the carbon-basedinorganic films 300 (coated film formation step) (see FIG. 11A).Thereafter, the opening KK is formed above the connection surface ofeach of the pad electrodes 111P to expose the connection surface(opening formation step) (see FIGS. 11B to 13E).

In the present embodiment, to form the openings KK, the resist patternRP is first formed (resist pattern formation step). In the presentembodiment, the resist pattern RP is so formed on the upper surface ofthe antireflection film 150 that the resist pattern RP has openingscorresponding to the connection surfaces of the pad electrodes 111P andcovers portions other than the connection surfaces (see FIGS. 11B and12C). The resist pattern RP is then used as a mask and the carbon-basedinorganic films 300 are used as etching stopper films to etch theantireflection film 150 and other coated films . The portions of theupper surfaces of the carbon-based inorganic films 300 that correspondto the connection surfaces of the pad electrodes 111P are thus exposed(etching step) (see FIG. 12D). In the present embodiment, the etching isperformed by using a fluorine (F)-based etching gas containing at leastone of CF₄, C₂F₆, C₃F₈, CHF₃, and SF₆. Ashing is then performed on theresist pattern RP and the portions of the carbon-based inorganic films300 that correspond to the connection surfaces of the pad electrodes111P so that they are simultaneously removed (ashing step) (see FIG.13E).

As described above, in the present embodiment, since the connectionsurfaces, which will be exposed, of the pad electrodes 111P are coveredwith the carbon-based inorganic films 300 in the dry etching process,the fluorine (F)-based etching gas does not directly come into contactwith the connection surfaces to be exposed. As a result, no compound(AlF_(x)) of aluminum and fluorine (F) is produced on the connectionsurfaces of the pad electrodes 111P, whereby the connection surfaces ofthe pad electrodes 111P are not contaminated.

In the present embodiment, the connection surface of each of the padelectrodes 111P therefore adequately establishes ohmic contact with anelectricity supplying metal configured as a connection means, such aswire bonding, whereby the solid-state imaging device operates normally.

Further, in the present embodiment, it is unnecessary to clean theconnection surfaces of the pad electrodes 111P. In addition to this, inthe present embodiment, ashing can be performed to simultaneously removethe resist pattern RP and the portions of the carbon-based inorganicfilms 300 that correspond to the connection surfaces of the padelectrodes 111P. Moreover, in the present embodiment, when the dryetching is performed, an end point in the dry etching process isdetected by monitoring a gas produced when the antireflection film 150and other coated films are etched. The device can therefore beefficiently manufactured in the present embodiment.

Further, in the present embodiment, the carbon-based inorganic film 300is formed on the upper surface of each of the pad electrodes 111P otherthan the connection surface electrically connected to an externalcomponent. The carbon-based inorganic film 300 is provided to preventthe incident light H from being reflected off the surface of the padelectrode 111P. In the present embodiment, the quality of capturedimages can therefore be improved.

The above advantageous effect will be described with reference to thedrawings.

FIG. 14 shows an overall configuration of a solid-state imaging device1J with no carbon-based inorganic film 300 provided on the surface ofeach of the pad electrodes 111P. FIG. 14 is a top view, as in FIG. 2.

FIGS. 15A and 15B diagrammatically show states in which the incidentlight H is incident on the two types of solid-state imaging device. FIG.15A shows a state in which the incident light H is incident on thesolid-state imaging device 1J (the one shown in FIG. 14) with nocarbon-based inorganic films 300 provided on the surface of each of thepad electrodes 111P. In contrast, FIG. 15B shows a state in which theincident light H is incident on the solid-state imaging device 1 (theone according to the present embodiment shown in FIG. 2) with thecarbon-based inorganic films 300 provided on the surface of each of thepad electrodes 111P.

When no carbon-based inorganic film 300 covers each of the padelectrodes 111P as shown in FIG. 14, the incident light H is reflectedoff the pad electrodes 111P, as shown in FIG. 15A. In this case, what iscalled a ghost phenomenon may therefore occur, and the quality ofcaptured images may be degraded in some cases.

In contrast, when the carbon-based inorganic films 300 cover the padelectrodes 111P in the solid-state imaging device 1 according to thepresent embodiment, the incident light H will not be reflected off thepad electrodes 111P, as shown in FIG. 15B.

In the present embodiment, what is called a ghost phenomenon willtherefore not occur, whereby the quality of captured images can beimproved.

The carbon-based inorganic films 300 are preferably made of graphite orany other suitable conductive material. In this case, no“electro-migration phenomenon” will occur in the pad electrodes 111P,whereby the reliability of the wiring can be improved.

The above advantageous effect will be described with reference to thedrawings.

FIG. 16 diagrammatically shows a state in which current flows through apad electrode 111P in the embodiment according to the presentdisclosure. FIG. 16 is a cross-sectional view taken along the line X1b-X2 b shown in FIG. 2, as in FIG. 6, and shows the portion where thepad electrode 111P is formed in the peripheral area SA of thesolid-state imaging device 1. FIG. 16 selectively shows a portion abovethe portion where the pad electrode 111P is formed in FIG. 6.

As shown in FIG. 16, a wire 502 is bonded to the surface of the padelectrode 111P that has been exposed through the opening KK, and currentsupplied through the wire 502 flows through the pad electrode 111P.

In this case, “electro-migration phenomenon”, in which aluminum atomsthat form the pad electrode 111P collide with electrons and the movedaluminum atoms cause disconnection, may occur in some cases. The“electro-migration phenomenon” typically tends to occur at the interfacebetween an insulating object and the pad electrode 111P because theactivation energy there is low. In the present embodiment, however, theconductive carbon-based inorganic film 300 is provided between the padelectrode 111P and the insulating passivation film 120. As a result, notonly does the current spread, but also the pad electrode 111P is not indirect contact with the insulating passivation film 120. In the presentembodiment, no “electro-migration phenomenon” will therefore occur,whereby the reliability of the wiring can be improved.

Further, in the present embodiment, since the carbon-based inorganicfilm 300 is provided on the upper surface of each of the pad electrodes111P, no “stress-migration phenomenon” will occur, whereby thereliability of the wiring can be improved.

When a force acts on any of the pad electrodes 111P made of aluminum orany other metallic material, the pad electrode 111P may break due toshear stress in some cases (“electro-migration phenomenon”). In thepresent embodiment, however, the carbon-based inorganic film 300functions as a buffer layer on the upper surface of each of the padelectrodes 111P, whereby no force directly acts on the pad electrode111P. In the present embodiment, no “stress-migration phenomenon” willtherefore occur, whereby the reliability of the wiring can be improved.

In addition to the above, when the carbon-based inorganic films 300 aremade of diamond-like carbon or any other material having high heatconductivity, heat generated in the solid-state imaging device 1 isefficiently transferred to the substrate 501 (see FIG. 1 and otherfigures). The reliability of the wiring can therefore be improved.

In the present embodiment, to remove the carbon-based inorganic film 300from part of the surface of each of the pad electrodes 111P, an O₂plasma-based ashing step is carried out. O₂ plasma makes the frontsurface of a semiconductor wafer hydrophilic. In the following rearsurface polishing step, in which a front surface protective tape thatprotects the front surface of the wafer is first removed, thehydrophilic front surface of the wafer allows the front surfaceprotective tape to be readily separated and the amount of residualadhesive resulting from the front surface protective tape to be greatlyreduced. Since the amount of residual adhesive can be greatly reduced,the yield of the device can be improved.

Further, when the O₂ plasma-based ashing is performed, the surface ofeach of the pad electrodes (made of aluminum or aluminum alloy) isoxidized. The oxidized surface does not allow oxidation on the aluminumcrystal grains to proceed but allows oxidation at the grain boundary toproceed. The progress of oxidation at the grain boundary reinforces thegrain boundary. In the following chip fragmentation step, in which thewafer is immersed in low specific resistivity pure water for a longperiod, the aluminum alloy containing copper (Cu), titanium (Ti), silver(Ag), silicon (Si), and other heterogeneous metals corrode due to abattery effect. That is, any base metal melts. For example, when copperand aluminum are contained, aluminum melts because aluminum is a basemetal. In the present embodiment, since the O₂ plasma-based ashing stepis the last wafer processing step, any of the heterogeneous metals or analloy of the aluminum and any of the heterogeneous metals that isexcessive and deposits along the grain boundary forms a thick oxidefilm. That is, since the thick oxide film prevents the aluminum alloyfrom coming into contact with the pure water, no battery effect orcorrosion occurs. As a result, a wire is bonded to the electrode in amore satisfactory manner, whereby the reliability thereof is improved inthe present embodiment.

To carry out the present disclosure, the embodiment described above isnot necessarily employed, but any other variety of variations can beemployed.

For example, a light guide (not shown) may be provided between the lightreceiving surface JS of each of the photodiodes 21 and the correspondingon-chip lens ML. The incident light H focused by the on-chip lens ML isguided through the light guide to the light receiving surface JS. Inthis case, a film made of a material of which the light guide is mademay be formed, and the film made of the material of which the lightguide is made in the peripheral area SA may be dry etched when theopenings KK are formed.

Further, the above embodiment has been described with reference to thecase where the pixel transistor is formed of the four transistors, thetransfer transistor, the amplifier transistor, the selector transistorand the reset transistor, but the pixel transistor is not necessarilyformed this way.

Further, the above embodiment has been described with reference to thecase where the solid-state imaging device is a CMOS image sensor, butthe solid-state imaging device is not limited to a CMOS image sensor butmay be a CCD image sensor.

Further, the above embodiment has been described with reference to thecase where the present disclosure is applied to a camera. The presentdisclosure is also applicable to other apparatus. For example, thepresent disclosure may be applicable to a scanner, a copier, and otherelectronic apparatus including a solid-state imaging device.

In the embodiment described above, the solid-state imaging device 1corresponds to the solid-state imaging device according to the presentdisclosure. Further, in the embodiment described above, the pixels Pcorrespond to the pixels according to the present disclosure. Further,in the embodiment described above, the substrate 101 corresponds to thesubstrate according to the present disclosure. Further, in theembodiment described above, the pixel array area PA corresponds to thepixel array area according to the present disclosure. Further, in theembodiment described above, the peripheral area SA corresponds to theperipheral area according to the present disclosure. Further, in theembodiment described above, the pad electrodes 111P correspond to thepad electrodes according to the present disclosure. Further, in theembodiment described above, the carbon-based inorganic films 300correspond to the carbon-based inorganic films according to the presentdisclosure. Further, in the embodiment described above, the passivationfilm 120, the planarization film 130, the lens material film 140, andthe antireflection film 150 correspond to the coated films according tothe present disclosure. Further, in the embodiment described above, theresist pattern RP corresponds to the resist pattern according to thepresent disclosure. Further, in the embodiment described above, thepassivation film 120 corresponds to the passivation film according tothe present disclosure. Further, in the embodiment described above, theplanarization film 130 corresponds to the planarization film accordingto the present disclosure. Further, in the embodiment described above,the lens material film 140 corresponds to the lens material filmaccording to the present disclosure. Further, in the embodimentdescribed above, the on-chip lenses ML correspond to the on-chip lensesaccording to the present disclosure. Further, in the embodimentdescribed above, the antireflection film 150 corresponds to theantireflection film according to the present disclosure. Further, in theembodiment described above, the camera 40 corresponds to the electronicapparatus according to the present disclosure.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2010-225090 filed in theJapan Patent Office on Oct. 4, 2010, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1.-7. (canceled)
 8. A solid-state imaging device comprising: a substratehaving pixels that receive incident light provided in a pixel arrayarea; pad electrodes formed in a peripheral area located around thepixel array area of the substrate; a carbon-based inorganic film formedon an upper surface of each of the pad electrodes but other than aconnection surface electrically connected to an external component; anda coated film that covers upper surfaces of the carbon-based inorganicfilms and has openings formed above the connection surfaces of the padelectrodes.
 9. An electronic apparatus comprising: a substrate havingpixels that receive incident light provided in a pixel array area; padelectrodes formed in a peripheral area located around the pixel arrayarea of the substrate; a carbon-based inorganic film formed on an uppersurface of each of the pad electrodes but other than a connectionsurface electrically connected to an external component; and a coatedfilm that covers upper surfaces of the carbon-based inorganic films andhas openings formed above the connection surfaces of the pad electrodes.